Your cervix is more selective than Berghain

Hello everyone, happy Friday!

On what I can only assume was a very slow news day, the Financial Times published a piece titled “How I got into Berghain, Berlin’s notoriously selective club.” That same day, we published a video about how sperm actually reach the egg. Reading one and watching the other, it struck me that the human cervix is every bit as selective as Berghain, with stricter criteria and worse lighting. So this week I am writing to you as a sperm. Consider it an instructive insight into how babies are actually made. And yes, it’s harder to make a baby than it is to get into Berghain.

So. Steve the Sperm has decided today is his day. He is getting into Egghain, the famously selective club that he and his c. 300 million friends are going to today.

Steve starts in the line (queue, for our British readers), which is to say the vaginal canal, where Steve is exposed to all the elements. The vagina is acidic and rich in Lactobacillus, precisely what you want if your priority is keeping infection out, and precisely what you do not want if you are a sperm (which today, we are). It is worse than that, actually: Lactobacillus physically sticks to sperm and drags their motility down. Vaginal secretions immobilise sperm within 1-2 hours. Fewer than 1% of Steve’s friends will reach the cervix at all. They will remain forever in the line. Steve, sensibly, decides to move up the line sharpish.

At the front of the queue is the notorious Egghain bouncer: cervical mucus. Famously picky, with criteria that are never published and are altered at the obscure pleasure of club management, the cervix. Steve adjusts his hair nervously (“is my forehead too big?”), but today Steve is lucky, because it is party time (read: ovulation), management is high on estrogen, and are therefore in a good mood. What this actually means is that the cervix (said management) is sitting higher in the vaginal canal, has softened, and its opening has relaxed. The cervical mucus has changed too, to that egg-white consistency everyone talks about. We’re going to explain why that matters (from Steve’s perspective – remember, we’re still a sperm).

When Steve sees cervical mucus, he sees a mesh net designed to keep him out. However, once every cycle the holes (technical term: pores) in the mesh change size. During ovulation, the pores are c. 8.4 micrometers. Outside of ovulation, they are 1.8 micrometers. Steve, famously, has a very large forehead (about 5 micrometers). Alas, this time, Steve will make it past the bouncers of Egghain. Lucky Steve. His friends may not be so lucky. The bouncers are still picky. Steve’s friends with abnormal heads, or tails that beat abnormally, cannot generate the movement to push through and are left outside in the elements. Womp womp.

Steve gets past. Hooray! However… He is not on the dancefloor yet. He has entered the crypt.

Yes, there is literally a crypt in your cervix, and yes, that is the actual anatomical term (badass). Crypts are tiny folds in the cervical canal where mucus pools and sperm shelter, and they are the reason for that half-remembered fact from school about sperm surviving inside you for up to 7 days. In 1980, one study found 200,000 sperm stored in the crypts after insemination.

So, Steve is effectively in the changing room (pivotal, for Egghain, because what one wears in the normal world is not what one wears in Egghain, oh no). In the crypt, Steve strips off his seminal plasma and his movement switches from a polite straight line to a weird, hyperactive dance move that looks like headbanging (also called capacitation). TLDR, Steve is pre-gaming.

Sidebar: What Steve just went through is what we call a ‘wash’, done in a lab before an IUI. Turns out our cervixes do it for us for free…

Steve has “camelled up” (a Boomer one for you, younguns), and is now on the dancefloor (read: the uterus). He moves fast here, he’s not interested in dancing on the uterus. He has a high pressure ‘Door number 1 or 2” decision to make. The signage is bad, and obviously he will not consult a map. Steve is deciding which fallopian tube (‘secret cool people back room’) to go to.

Steve has picked the correct door. Woo! He is close to the heart of Egghain, the egg! Now, one might think of the egg as a sort of Queen Bee, passively waiting to be found. Wrong. Her cumulus cells (read: thrifted and very cool jacket) are releasing progesterone, which changes how Steve moves (sweet, he’s matching his dance moves).

Our queen will only let one in. Steve is close, but at the end of the day, it’s her choice. Indeed, a growing body of research is demonstrating that an egg has an actual, chemical preference researchers call ‘cryptic female choice’ (iconic).

Steve, unproblematic king that he is, has made it. Made the line (vaginal canal), got past the bouncer (cervical mucus), was accepted in by club management (cervix) and got into the changing room (cervical crypts), zoomed past the dancefloor (uterus), into the secret room at the back (fallopian tube), and made it to the heart of Egghain. He is staring down the famous Egghain egg. Whether or not he is chosen… well, let’s leave that to y’all’s imagination.

Biology is cool y’all. Steve’s odyssey is also the entire thesis behind what we build. If cervical mucus is the lab, the job is to get sperm to it quickly and in one piece, which is why the Béa applicator holds a semen sample against the cervix instead of leaving it in the vaginal canal, and delivers 3.23 times more sperm to the cervix than sex does.

Here’s to Steve, and to all the other Steves who will make it this weekend.

Take care of yourself.

Tess

Co-Founder & CEO